Rheostat



Oct. 16, 1923. 1,470,758

6. M. LITTLE RHEOSTAT Filed Nov. 29, 1920 a 9 i} w%@@@@%@@ 4 H 3.

- WITNESSES: INVENTOR George M. Liffle ATTORNEY Patented Oct. 16, 1923.

UNITED STATES PATENT OFFICE.

GEORGE M. LITTLE, or PITTSBURGH, PENNSYLV NIA; AssIeNoR r0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF P NNSYLVANIA RHEOsrAT.

Application filed November 29, 1920.

T 0 all whom it may concern:

Be it known that I, GEORGE M. LrrrLE, a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Rheostats, of which the following is a specification.

My invention relates to rheostats and it has particular relation to the form and construction of resistance rods or bars forming parts thereof.

he object of my invention is to provide a rheostat which will not vary its resistance or become impaired after being operated for a considerable period of time.

Heretofore, after a rheostat of the type in question had been operated for a considerable period a deposit of metal was formed upon the resistance rods or members, caused by the abrasion of the slidable contact member. This coating is a good conductor and will furnish a path for the electric current of less resistance than that through the resistance material and, eventually, will vary the resistance values of the rheostat to an undesirable degree.

Briefly speaking, my invention consists in providing resistance rods or bars of relatively high-resistance material, coverin the contact surface of each with a strip 0 metallic material and then cutting slots or depressions through the metallic coating into the resistance material.' These slots prevent the current from uninterruptedly traversing the resistance coating.

Referring to the accompanying drawing, Figure 1 is a view, in side elevation, of a rheostat embodying my invention.

Fig. 2 is a View, partly in section and partly in end elevation, of the apparatus that is shown in Fig. 1, taken along the line 11-11, thereof.

Fig. 3 is a plan view, of a part of the apparatus that is shown in Fig. 1.

Referring to Figs. 1 and 2, a rheostat 1 comprises a base member 2 having turnedupsides 3. A member or rod 4, of relatively high-resistance material, is supported on the base member 2 by means of resilient members or clips 5, which are mounted upon insulating blocks 6. The resistance rod 4 has a strip of preferably sprayed or plated metalcoating 8 upon its Contact sur- Serial No. 426,920.

face, and slots 9 are cut diagonally across this coating into the resistance rod 4.

A contact member 11 for shunting the resistance rod 4 is slidably mounted above the rod 4 upon a pair of rods 12, each of which is covered with an insulating wrapper or cover 13. A strip of copper, or some other good conductor 14, is so positioned upon the slidable Contact member 11 that it makes good electrical contact with the metallic coating 8.

A suitable Contact terminal 15 is mounted upon the slidable Contact member 11 and is electrically connected to the copper Contact strip 14. One end of the resistance rod 4 is electrically connected to a suitable stationary terminal 16.

Installation of the rheost-at is effected by connecting the contact terminals 15 and 16 to conductors forming a part of the circuit in which the rheostat is to operate. Resistance rod 4 may be inserted into the circuit by actuating the slidably mounted member 11 in a direction away from the stationary contact terminal 16. The resistor 4 may be gradually shunted or excluded from circuit y actuating the slidable contact member 11 toward the stationary contact terminal 16.

One ofthe principal features of my invention is the use of the grooves 9 in the rods 4, which prevent a deposit of copper from the copper strip 14 from forming a conductor along the entire contact surface of the resistor 4. This deposit of copper is caused by the resistor 4 having relatively high abrasive properties. It would be possible to have the grooves 9 extend completely around the resistance rod 4 and not to employ the metallic coating 8. The purpose of the preferably sprayed or plated metallic coating 8 is to afford ood contact between the copper plate 14 and the resistor 4.

While I have shown a simple and preferred form of my invention, it is not limited to the particular structure employed to illustrate it, but may be subjected to numerous minor modifications. For example, a plurality of resistance rods 4 may be mounted in side-by-side relation and a shunting device operated to engage them. Moreover, a rheostat of the well-known dial or face-plate type may be constructed to embody these features. It would comprise an arcuate resistance member having slots or grooves extending across its contact surface and a rotatably mounted arm for shunting the resistance member. I desire, therefore, to be limited only by the scope of the appended claims, as indicated by the terms thereof.

I claim as my invention:

1. A resistance member having grooves therein, saidgrooves extending across the surface of said resistance member.

2. A resistance member havin grooves therein, said grooves extending iagonally across the contact surface of said resistance member.

3. A rod of relatively high-resistancefmaterial, having a portion of its surface covered by a metal of relatively low resistance and havin grooves extending across its surface.

4. g bar of relatively high-resistance material having a portion of its surface covered by a metal of relatively low resistance and having grooves extending diagonally across its surface.

5. In a rheostat, the combination with a member of relatively high-resistance material having a plurality of slots extending across its contact surface, of a relatively movable member for shunting said resistance member.

6. In a rheostat, the combination with a member of relatively high-resistance having a plurality of grooves extending diagonally across its contact surface, of a movable member for shunting said resistance member.

7 In a rheostat, the combination with a member of relatively high resistance having a plurality of depressions-extending across its contact surface, and means for shunting said member, of means comprising a good conducting material covering said member between said depressions for affording good contact between said member and said shunting means.

8. In a rheostat, the combination with a resistance rod, having a plurality of notches extending across its contact surface, and a metallic coating between said notches, of a contact member slidably mounted for shunting said rod.

9. The method of forming a resistance rod comprising coating said rod with a conducting material and then cutting depressions through said material into said rod.

10. The method of forming a resistance rod comprising making depressions along the contact surface of said rod and covering portions of said rod between said depressions with a metallic covering.

In testimony whereof, I have hereunto subscribed my name this 18th day of November, 1920.

GEORGE M. LITTLE. 

